Group 1 - The naming rules for train numbers are closely related to the running directions of "up" and "down" [2] - Trains heading towards Beijing are classified as "up" and assigned even numbers, while those moving away from Beijing are classified as "down" and assigned odd numbers [2] - For example, a train from Zhengzhou East to Anyang East is an "up" train with the number G6666, while the return train from Anyang East to Zhengzhou East is a "down" train with the number G6665 [2] Group 2 - The letter prefix in train numbers has specific meanings, such as G for high-speed trains, C for intercity trains, D for动车组 trains, Z for direct express trains, T for express trains, and K for fast trains [3] - The numbering system allows dispatchers to quickly identify the type, grade, and task of any train operating on the line [2]

Group 1 - The naming rules for train numbers are significant, with specific letters indicating different types of trains, such as G for high-speed trains, C for intercity trains, D for动车组 trains, Z for direct express trains, T for express trains, and K for fast trains [1] - Train number assignment is closely related to the direction of travel, with even numbers assigned to trains heading towards Beijing (upward direction) and odd numbers for those traveling away from Beijing (downward direction) [3]